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UPDATE on Cleaning Diasel fuel tanks

I would like to report on how I did last summer on welding a crack in my diesel aluminum fuel tank on my tuna boat. I am alive and well. Welding from the inside was the only way. There was a 24" hole for cleaning so I did not need to cut a hole. First I cleaned with a water based cleaner. Next I wire brushed the entire tank. Tank seemed good and clean to me. Next I bought a RAE Systems UltraRAE 3000 VOC tester. This was for testing to see if I needed to clean further. On the first test I had 15PPM. This is very clean. My CNC machine shop at the end of the day reads 30PPM. So I was good to go. It was tight working inside but had no choice. I did use a Hooka for breathing air AND IT WORKED GREAT. My helper would turn a large blower on as soon as I stopped welding , than off as I started again. All seams have three full beads over the old. It took about six hours of weld time but I am happy with how it turned out. The VOC tester did cost $5500. but took the guess work out.

I repair aluminum diesel tanks from time to time, some full of fuel. I always purge with argon for a few minutes before and during welding. Since you already had a S.C.B.A. I would of purged a full bottle in it, welded it and charged you have the price of the meter. You couldn't rent a meter?

As a teenager, several people I knew had Jeeps, those who didn't had equally rusty cars. Leaky gas tanks were more common than Subarus are today. My first leaky gas tank project we flushed with water for hours. As an invincible teenager I was confident it was adequately clean. My father was not in favor, he wanted my buddy to buy a new tank. Since I was going ahead anyway, he proposed I use only a soldering copper. You heat a 2 pound piece of copper on a handle, tin it with solder, use it to heat the flux coated steel tank to solder. Problem is the copper only stores a limited amount of heat, it's at its best when you replenish the heat with the torch while soldering.
BANG!
I think those tanks are supposed to hold 10 gallons, that one now holds 13! We had to make a new hold down strap, but he drove it for years.
Next round I used a different technique. Filling the tank full of water with the small port in the bottom open to drain slowly, I set fire to the open filler neck, This produced a lazy flame a couple inches high as the tank drained, lack of air inside kept the flame at the opening as residual gas evaporated from the walls of the tank. It burned for an amazing 1/2 hour! DON'T TRY THIS AT HOME! I AM AN EXPENDABLE HUMAN BEING!

If i could not have crawled inside I could have never cleaned the tank good enough to ever weld in it. The RAE 3000 VOC meter is a great tool , easy to learn. I will sell it at some point for much less than I paid for it. It will be listed here first as there could be others that are in need like I was. When I crawled out of that tank for the last time I sure felt good. I never gave it time to build up any fumes from welding. Every 5"-7" I would stop and the blower would push the dirty air out in about 1 min than back to wielding. I think I put 20# of wire in that tank. For anybody else that may have the same problem , if you can get inside the diesel tank to clean it than you will be fine. If you have the right tools for testing for VOC than you will be safe. I never thought I would learn so much about aluminum welding when I bought my boat.
Kevin

An old friend was in failing health. For 80 years he had been an inventor and a brilliant child, surrounding himself with wonderful toys, and items he intended to re purpose into machines that would win him recognition among the great inventors from history. They cheated, and started hundreds of years ahead of him. He had steam engines I had never heard of, organs that played themselves, a machine shop we would all envy. There were hundreds of inventions started but not finished, others not yet started. Neighbors, Town, State, and wife conspired against him and insisted what couldn't be fit into the 20000 square foot building had to go. My son and I did the job. One of his inventions was to use a 10000 gallon fuel tank. It contained maybe 15 gallons of #4 Fuel. A sample of this sludge seemed not very volatile. I cut a 3x4' hole in the end of the tank. I could bale it out, wasting time, or burn it. I splashed a bit on the wall of the tank and lit it with the cutting torch. It started small, ultimately flame 5' in diameter shot horizontally 10' before curling skyward, and rising to a height of 20'. It roared like a jet, black smoke was incredible! I stood there waiting for the police! Some nosy neighbors came to watch, no police! an hour later it burned out.

I've repaired (cracks and punctures) or otherwise modified or added fittings to a number of those round aluminum diesel full tanks (like you see on semi trucks) over the years. Always had the customer take it off the truck and bring it to me. I'd just take them to the local car wash and wash them out with the spray wand using the de-greaser, soap and rinse cycles. Also did the outside of the tank to get all the road grime off. I never "sniffed" them before welding with any thing other than my nose. Never got any unpleasant surprises that I can recall.

The following is from the US Navy's "Ten Commandments of Welding Safety" ....

"Thou shall not weld on un-purged tanks that have held combustible materials lest thy friends end up consoling thy widow in ways generally unacceptable to thee."

I've repaired (cracks and punctures) or otherwise modified or added fittings to a number of those round aluminum diesel full tanks (like you see on semi trucks) over the years. Always had the customer take it off the truck and bring it to me. I'd just take them to the local car wash and wash them out with the spray wand using the de-greaser, soap and rinse cycles. Also did the outside of the tank to get all the road grime off. I never "sniffed" them before welding with any thing other than my nose. Never got any unpleasant surprises that I can recall.

The following is from the US Navy's "Ten Commandments of Welding Safety" ....

"Thou shall not weld on un-purged tanks that have held combustible materials lest thy friends end up consoling thy widow in ways generally unacceptable to thee."

I like your Navy quote, and agree with all the precautions suggested. That said, old oil and propane tanks are a resource I can't pass up. I've built pilings to build a building on, a dock, 20 giant ash trays I use for excavating, (put dirt in them while digging a trench, then use a 4 hook sling to lift them and dump it back in the ditch. It reduces the lawn repair to 1/3.) I built a dump trailer for a compact utility tractor,... the uses are limited only by imagination! I've never had a mishap with an oil tank or propane tank cut. Precautions must be used.